The pill, called Vibratory Ingestible BioElectronic Stimulator, or VIBES for short, stimulates nerve endings that sense stomach expansion, tricking the brain into thinking the stomach is full. 

"The capsule, about the size of a large vitamin, houses a tiny motor that starts vibrating when it hits the stomach, stimulating the organ’s stretch receptors," according to MIT Technology Review magazine.

Vibrating Capsule Being Tested as Weight-Loss Drug (foxbusiness.com)